Post-retirement benefits - Summary of fair value of plan assets (Detail)	Dec. 31, 2021	Dec. 31, 2020
Disclosure of information about defined benefit plans [abstract]
Equities	17.60%	21.10%
– Quoted	13.40%	17.90%
– Private	4.20%	3.20%
Bonds	60.20%	55.80%
– Government fixed income	23.20%	17.70%
– Government inflation-linked	9.50%	9.60%
– Corporate and other publicly quoted	20.60%	22.60%
– Private	6.90%	5.90%
Property	7.90%	7.50%
– Quoted property funds	3.40%	3.10%
– Unquoted property funds	4.50%	4.40%
Qualifying insurance policies	10.50%	11.30%
Cash & other	3.80%	4.30%
Total	100.00%	100.00%

The percentage cash and cash equivalents contribute to the fair value of defined benefit plan assets. [Refer: Cash and cash equivalents; Plan assets, at fair value; Defined benefit plans [member]] [Contrast: Cash and cash equivalents, amount contributed to fair value of plan assets]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2021-01-01
-Paragraph 142
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2021-en-r&anchor=para_142_a&doctype=Standard
-URIDate 2021-03-24